a. Field of Invention
The invention relates generally to shock absorption, and, more particularly to an improved apparatus and method for the absorption of horizontal and vertical impact forces in a wheelchair during travel over rough or uneven surfaces.
b. Description of Related Art
Wheelchairs include various components which are subject to high impact forces that directly affect wheelchair comfort and durability. In order to improve wheelchair ride and comfort, and to avoid secondary injuries due to extended wheelchair use, wheelchair components must be designed to eliminate or reduce the effect of such impact forces. Common secondary injuries due to extended wheelchair use include, for example, musculoskeletal injuries such as herniated discs, spinal deformities and chronic low back pain, as well as neurological injuries. Additionally, common wheelchair component durability issues include premature wheelchair frame deterioration, or complete component failure due to fatigue.
When traveling over obstacles, the impact forces described above are generally transferred through the wheels and caster fork, through the frame, through the seat cushion and to the body of a user. Typical impact forces, such as forces generated by wheels traveling over a rough surface, include both horizontal and vertical force components relative to the travel surface. Accordingly, one area of specific concern is wheelchair caster forks, which experience both the horizontal and vertical impact forces through the wheels during wheelchair travel over rough surfaces.
In an effort to reduce impact forces, conventional wheelchair designs have included caster fork designs including vertical shock absorbers for shock absorption perpendicular to the travel surface. Likewise, caster forks have been designed to include horizontal shock absorbers for shock absorption parallel to the travel surface. In order to target both vertical and horizontal impact forces, it is apparent that caster forks can be designed with both vertical and horizontal shock absorbers. However, such caster fork designs have thus far had drawbacks related to functionality, efficiency, durability and aesthetics.
In the art, there presently exist conventional casters for targeting both vertical and horizontal impact forces, as disclosed in U.S. Pat. No. 1,745,992 to Herold and U.S. Pat. No. 6,149,169 to Chelgren.
U.S. Pat. No. 1,745,992 to Herold discloses a mechanism that employs a resilient rubber block for shock absorption of both vertical and horizontal impact forces. Herold however does not address shock absorption for wheelchair and other related applications, in which the impact forces are relatively large in the vertical and horizontal directions. Moreover, the rubber block for Herold only absorbs a fraction of the entire vertical and horizontal impact forces, and is inefficient in absorbing and targeting the entire component of such forces. Likewise, U.S. Pat. No. 6,149,169 to Chelgren discloses a caster fork design for shock absorption of both vertical and horizontal impact forces. As for Herold, the shock absorption mechanism for Chelgren also does not effectively absorb or target the entire component of the vertical and horizontal impact forces.
For the U.S. patents cited above, from a design and effectiveness standpoint, the design of the shock absorption mechanisms described above has left a need for improvements for effectively targeting and absorbing the entire component of the vertical and horizontal impact forces. From an assembly standpoint, the assembly and installation of complex shock absorption systems can be time-consuming and burdensome, and can further add to the overall cost of the end-product. Lastly, from a maintenance and use standpoint, improvements in conventional shock absorption systems would likewise provide improvements in the durability of wheelchairs and other such devices.